Aqueous compositions for sizing of paper

ABSTRACT

The present invention provides a paper sizing composition which comprises a sizing agent selected from cyclic dicarboxylic acid anhydride or alkyl ketene dimer, a stabilizing and/or dispersing agent which is an amphoteric polymer and a polyaluminum compound.

The present invention relates to water based compositions of syntheticcellulose-reactive sizing agents, which are alkyl ketene dimers orcyclic dicarboxylic acid anhydrides and more particularly to suchcompositions which contain an amphoteric polymer and a polyaluminiumcompound.

Alkyl ketene dimers (AKD) and cyclic dicarboxylic acid anhydrides,particularly alkenyl succinic anhydride (ASA), are to a great extentused for paper sizing, hydrophobing, at neutral or alkaline pH. Thecompounds are cellulose reactive and bind directly to the hydroxylgroups in the cellulose. The commercially used products are usuallystabilized with cationic starch which also contributes to retention ofthe sizing agent. Separate additions of retention agents and otherchemicals to the stock are often also used to increase retention and toimprove the sizing. It is known to use the sizing agents in combinationwith aluminium compounds. Small amounts of alum are often used forASA-emulsions, either in the emulsion or as separate stock addition,primarily to decrease the deposition problems which are connected withthis. The production of sized paper by stock addition of cationicAKD-dispersion, high cationized starch and water soluble aluminium saltis described in the Japanese patent application 84-199900. It is alsoknown from the German patent application 4090740 to incorporate apolyaluminium compound in dispersions of AKD and cationic dispersingagent such as cationic starch. D-based sizing compositions arecomparatively expensive due to the costs for the ketene dimer as suchand the development is thus directed to production of dispersions whichgive the best sizing with the lowest amount of AKD. Requirements are ofcourse also made on the dispersions as such with regard to stability andsatisfactory high dry contents.

According to the present invention it has been found that water basedcompositions of ketene dimers or cyclic dicarboxylic acid anhydrideswhich comprise both an amphoteric polymer and a polyaluminium compoundgive very good sizing with low amounts of the sizing agent since theygive good retention of this and since they also positively contribute togeneral retention of fibres and fillers and to dewatering effect atpaper production. They also have good effect in the presence ofretention/dewatering systems which are based on anionic inorganiccolloids, such as silica based colloids, and cationic polymers.

The present invention thus relates to aqueous compositions of sizingagents which are hydrophobing cyclic dicarboxylic acid anhydrides oralkyl ketene dimers, which compositions comprise an amphoteric polymer,which is amphoteric starch or an amphoteric acrylamide based polymer,and a polyaluminium compound.

The two types of sizing agents are per se well known. Cyclicdicarboxylic acid anhydrides can be characterized by the general formula##STR1## wherein R₂ is a dimethylene or trimethylene radical and R₁ is ahydrocarbon group having more than 7 carbon atoms and can be an alkyl,alkenyl, aralkyl or aralkenyl group. The cyclic dicarboxylic acidanhydrides which are used commercially to the greatest extent are alkyland alkenyl succinic anhydrides (ASA) and particularly isooctadecenylsuccinic anhydride.

Alkyl ketene dimers have the general formula ##STR2## wherein R₁ and R₂are hydrophobic hydrocarbon groups having about 6 to about 30 carbonatoms and which are usually alkyl groups having 12 to 20 carbon atoms,such as hexadecyl and octadecyl groups.

The amphoteric polymer in the present compositions are amphoteric starchor amphoteric acrylamide based polymer. The term amphoteric hereinrefers to polymers containing both anionic and cationic groups.Amphoteric starch is preferred and for this the anionic groups can forexample be phosphate, phosphonate, sulphate, sulphonate or carboxylicacid groups and they are preferably phosphate groups. The cationicgroups are tertiary amino groups or quaternary ammonium groups. Theratio between the number of anionic and cationic groups in the starchcan be within the range 0,025:1 to 90:1, and is preferably within therange 0.4:1 to 40:1. Any starch which contains both these types ofgroups can be used and the starch itself can thus originate frompotatoe, corn, wheat, tapioca, rice, waxy maize etc. The anionic groupsin the starch can be native and/or introduced by chemical treatment ofthe starch. It is particularly suitable to use cationized potato starchsince native potato starch contains a substantial amount of covalentlybound phosphate monoester groups.

The amphoteric polymer can also be an acrylamide based polymer, whichare water soluble polymers with acrylamide and/or methacrylamide as themain monomeric unit. These polymers can have molecular weights fromabout 10000 to about 1500000, suitably from about 300000 to about800000. Amphoteric acrylamide based polymers can be prepared byintroduction of ionic groups in a polymer containing (meth) acrylamideas the main component. Cationic groups can be introduced by differentmethods such as Hofmann-degradation and Mannich reaction and anionicgroups can for example be introduced by hydrolysis or sulphomethylationreaction. Amphoteric acrylamide based polymers can also be prepared byco-polymerisation of (meth) acrylamide and a monomer mixture containingboth anionic and cationic monomers.

In the present compositions both an amphoteric polymer and apolyaluminium compound are included. It is believed that there is acertain interaction between the anionic groups in the amphoteric polymerand the polyaluminium compounds which contributes to a goodstabilisation of the compositions and good retention of the sizing agentin the stock.

Ketene dimers are the preferred sizing agents. Aqueous AKD-dispersionswhich comprise both an amphoteric polymer and a polyaluminium compoundgive very good sizing with low amounts of AKD and the dispersionsfurther have satisfactory stability and can be produced withsufficiently high dry contents for commercial use. The dispersions alsohave good effect in the presence of retention/dewatering systems whichare based on combinations of anionic inorganic colloids, such as silicabased colloids, and cationic polymers. It also seems that thedispersions as such can contribute to an improvement of dewatering andgeneral retention of fibres and optional fillers.

Polyaluminium compounds are based on aluminium, hydroxy groups andanions, they are termed basic and in aqueous solutions they arepolynuclear complexes. Polyaluminium compounds such as polyaluminiumchloride and polyaluminium chloride containing sulphate are inthemselves well-known compounds and have in connection with paper beenused, among other things, at rosin sizing for fixation of the rosin byformation of aluminium-rosin complex.

As examples of suitable compounds can be mentioned polyaluminiumcompounds having the general formula

    Al.sub.n (OH).sub.m X.sub.3n-m

wherein X is a negative ion such as chloride or acetate and both n and mare positive integers so that 3_(n-m) is greater than 0. PreferablyX=Cl⁻ and such polyaluminium compounds are known as polyaluminiumchlorides (PAC). Polyaluminium chlorides can also contain anions fromsulphuric acid, phosphoric acid, polyphosphoric acid, chromic acid,dichromic acid, silicic acid, citric acid, carboxylic acids or sulphonicacids.

The basicity of polyaluminium compounds of the above given formula isdefined as the ratio m/3n^(*) 100. The basicity is suitably within therange from 10 up to 90% and preferably within the range from 20 up to85%.

The most suitable polyaluminium compounds in the present compositionsare polyaluminium chlorides, polyaluminium chlorides containing sulphateand polyaluminium sulphates. As examples of polyaluminium sulphates canbe mentioned those with the formula [Al(OH)_(x) (SO₄)_(y) (H₂ O)_(z)]_(n) wherein x has a value of 1.5 to 2.0, y a value of 0.5 to 0.75,x+2y=3 and z=1.5-4, suitably 1.5-3.0. The term polyaluminium compoundsis herein used to encompass also mixtures and co-condensates of cationicdicyandiamide resins and polyaluminium compounds. Such products aredisclosed in the European patent application 320986.

An example of a commercially available polyaluminium compound isEkoflock, produced and sold by Eka Nobel AB in Sweden. In this case thebasicity is about 25% and the content of sulphate and aluminium about1.5 and 10 per cent by weight, respectively, whereby the content ofaluminium is counted as Al₂ O₃. In aqueous solutions the dominatingcomplex is Al₃ (OH)₄ ⁵⁺ transformed into Al₁₃ O₄ (OH)₂₄ ⁷⁺.

Other examples of commercially available compounds are the sulphate-freeSachtoklar®, sold by Sachtleben Chemie in Germany, thesulphate-containing WAC sold by Atochem in France, the highly basicpolyaluminium chloride compound Locron sold by Hoechst AG in Germany,poly(hydroxyaluminium) sulphate Omniklir, sold by OmniKem, USA,Niaproof, which is an aluminium hydroxy acetate, sold by Niacet in theUSA and Alzofix which is based on polyaluminium chloride anddicyandiamide, sold by SKW Trostberg, Germany.

In the ketene dimer dispersions according to the present invention theamphoteric polymer is suitably present in amounts of from 1 to 35% byweight, based on the ketene dimer. The amount is preferably within therange of from 5 to 20. The polyaluminium compound is present incomparatively high amounts and suitably in an amount of from 0.1 to 10%by weight, calculated as Al₂ O₃ on the ketene dimer, and preferably theamount of polyaluminium compound is within the range of from 1 to 6% byweight. Despite the high amounts of aluminium compound the dispersionsshow good stability. Dispersions according to the present invention canhave AKD contents of from about 5% by weight up to about 30% by weightand the content of AKD is suitably within the range of from 10 to 20%.

Ketene dimer dispersions according to the present invention can beproduced by mixing an aqueous solution of the amphoteric polymer withAKD-wax at a temperature of from about 55° C. to about 95° C. andhomogenizing at this temperature under a pressure of from about 50 toabout 500 bar. The obtained emulsion, which has a drop size of fromabout 0.3 to about 3μm, is then rapidly cooled and the polyaluminiumcompound is suitably added during or after the cooling. In addition tothe three above mentioned essential components other components can alsobe incorporated into the dispersions, for example anionic surface activeagents such as sodium lignosulphonate, extenders such as urea and ureaderivatives etc.

Cyclic dicarboxylic acid anhydrides such as ASA are liquid at roomtemperature. In commercial ASA-products an emulsifier is usuallypresent. Aqueous compositions of cyclic dicarboxylic acid anhydrides areemulsions and compositions according to the invention can be prepared bymixing the liquid acid anhydride with a solution of the amphotericpolymer, whereby the polyaluminium compound is present in the solution.The solution should be kept at a temperature of about 20° C.Compositions of cyclic dicarboxylic acid anhydrides according to theinvention suitably contain the acid anhydride and the amphoteric polymerin a weight ratio of from 1:1 to 1:4. The polyaluminium compound ispresent in corresponding amounts, based on the cyclic dicarboxylic acidanhydride, as given for the ketene dimer dispersions. ASA-emulsions arenormally produced at the paper mill in direct connection to its use assizing agent at the paper production. Amounts of the acid anhydride offrom about 0.1 to 5% by weight are then common.

The compositions according to the invention are used in a conventionalmanner at the production of paper. They can be used both for surfacesizing and stock sizing at the production of paper, board and cardboard.The present invention also relates to a method for the production ofpaper using aqueous compositions of cyclic dicarboxylic acid anhydridesor alkyl ketene dimers containing amphoteric polymer and polyaluminiumcompound, as described above, as surface- or stock sizing agents. Atstock sizing the composition are suitably added to an amount of AKD orcyclic dicarboxylic acid anhydride of 0.2 to 8 kg/ton of the dry contentof the stock, ie fibres and optional fillers, where the dosage is mainlydependent on the quality of the paper.

The invention is further illustrated in the following examples which,however, are not intended to limit the same. Parts and per cent relateto parts by weight and per cent by weight respectively, unless otherwisestated.

EXAMPLE 1

Ketene dimer dispersions according to the invention were prepared asfollows: 70 g of a potato starch cationized to a degree of substitutionof 0.042 were mixed with 450 g of AKD-wax and about 2340 g of watercontaining 15 g of sodium lignosulphonate at a temperature of 75° C. andthe mixture was homogenized at this temperature under a pressure of 200bar and rapidly cooled. During the cooling a polyaluminium compound wasadded. For dispersion 1a) 120 g of a polyaluminium chloride containingsulfate, Ekoflock from Eka Nobel AB, were added. For dispersion 1b) 168g of a polyaluminium sulphate, Omniklir from OmniKem, USA, correspondingto 2.8 per cent of Al₂ O₃, were added. For dispersion 1c) 150 g ofAlzofix P (dicyandiamide-polyaluminium condensate) from SKW Trostberg,Germany, corresponding to 2.8 per cent of Al₂ O₃, were added.

EXAMPLE 2

Paper sheets were prepared from a standard stock of bleached sulphatepulp (48% birch, 32% pine and 20% calcium carbonate) at a pH of 8.0according to the standard method SCAN-C23X for laboratory scale. In thetable below Cobb-values, measured according to Tappi standard T 441OS-63 are shown. In these tests Dispersion 1a) according to theinvention was compared with a dispersion, Ref., containing cationic waxymaize starch and the same polyaluminium compound as in dispersion 1a)and the starch and the polyaluminium compound were present in the sameamounts as in dispersion la).

    ______________________________________                                        Dispersion      AKD     Cobb 60                                               no.             kg/t    g/m.sup.2                                             ______________________________________                                        1a)             0.3     33                                                    1a)             0.4     25                                                    1a)             0.5     23                                                    1a)             0.6     22                                                    Ref.            0.3     65                                                    Ref.            0.4     30                                                    Ref.            0.5     25                                                    Ref.            0.6     25                                                    ______________________________________                                    

As evident AKD-dispersions containing polyaluminium compound wherein thestarch is amphoteric are considerably more effective than productswherein the starch contain only cationic groups.

EXAMPLE 3

The sizing effect of the dispersions 1b) and 1c) were investigated inthe same manner as in Example 2 and the following results were obtained:

    ______________________________________                                        Dispersion      AKD     Cobb 60                                               no.             kg/t    g/m.sup.2                                             ______________________________________                                        1b)             0.3     34                                                    1b)             0.4     28                                                    1b)             0.5     24                                                    1b)             0.6     23                                                    1c)             0.3     30                                                    1c)             0.4     24                                                    1c)             0.5     24                                                    1c)             0.6     23                                                    ______________________________________                                    

EXAMPLE 4

In this example edge penetration values were investigated for a 35% H₂O₂ -solution by means of a so-called Edge Wick test. The tests were madeon a stock from 100% CTMP-pulp from which paper having a basis weight of150 g/m² were prepared at a pH of 7.6. In all tests alum, polyamidoaminewet-strength resin and a dewatering-retention system based on silica Soland cationic starch were added to the stock separately from theAKD-dispersion. A comparison was made between dispersion 1a) accordingto the invention and a standard AKD-dispersion containing cationic waxymaize starch Ref. 1 and also with a dispersion corresponding to la) butnot containing polyaluminium compound, Ref. 2.

    ______________________________________                                                        AKD     H.sub.2 O.sub.2                                       Dispersion      kg/t    kg/m.sup.2                                            ______________________________________                                        1a)             1       3.35                                                  1a)             1.5     2.58                                                  1a)             2       1.49                                                  1a)             3       1.57                                                  Ref. 1          1       3.95                                                  Ref. 1          1.5     3.20                                                  Ref. 1          2       2.33                                                  Ref. 1          3       2.14                                                  Ref. 2          1       3.88                                                  Ref.2           1.5     3.06                                                  Ref. 2          2       2.30                                                  Ref. 2          3       2.14                                                  ______________________________________                                    

As evident the dispersions according to the invention gave a clearlyimproved sizing in this respect in comparison with a standard product.It is also evident that this effect is not solely dependent on the typeof starch but it is dependent on the combination of amphoteric starchand polyaluminium compound.

EXAMPLE 5

For the same stock as above dewatering tests were carried out in thepresence of a commercial retention- and dewatering system, Compozil®,which comprises inorganic silica sol (Si-sol) and cationic starch (CS)which are added to the stock separately. The tests were made using thissystem in the presence of different ketene dimer dispersions and thedewatering effect was measured by means of a "Canadian Standard Freeness(CSF) Tester" which is the usual method for characterizing dewatering ordrainage capacity according to SCAN-C 21:65. For O-test, stock withoutaddition of either the retention-dewatering system (R-D system) orAKD-dispersions the dewatering capability was 310 ml CSF. Tests weremade with dispersions 1a) and 1b) according to the invention andcomparisons were made with a reference dispersion, a standardD-dispersion containing cationic waxy maize starch.

    ______________________________________                                        Dispersion AKD     RD system        CSF                                       no.        kg/t    CS kg/t    Si-sol kg/t                                                                           ml                                      ______________________________________                                        --         --      4          1       550                                     --         --      6          1       580                                     --         --      8          1       575                                     1a)        1       4          1       580                                     1a)        1       6          1       615                                     1a)        1       8          1       590                                     1b)        1       4          1       570                                     1b)        1       6          1       600                                     1b)        1       8          1       590                                     Ref.       1       4          1       540                                     Ref.       1       6          1       575                                     Ref.       1       8          1       570                                     ______________________________________                                    

As can be seen the dispersions according to the invention gave animprovement of the dewatering effect while the reference dispersion gavea slight impairment of this.

We claim:
 1. An aqueous sizing composition which comprises a sizingagent which is selected from the group consisting of cyclic dicarboxylicacid anhydride and alkyl ketene dimer, a stabilizing and/or dispersingagent which is an amphoteric polymer selected from the group consistingof amphoteric starch and amphoteric acrylamide based polymer, and apolyaluminum compound.
 2. The composition of claim 1 wherein theamphoteric polymer is amphoteric starch.
 3. The composition of claim 2wherein the amphoteric starch is cationized potato starch.
 4. Thecomposition of claim 1 wherein the polyaluminium compound ispolyaluminium chloride, sulphate-containing polyaluminium chloride,polyaluminium sulphate or a mixture or co-condensate of cationicdicyandiamide resin and a polyaluminium compound.
 5. The composition ofclaim 4 wherein the polyaluminium compound is present in an amount offrom 0.1 to 10% by weight, calculated as Al₂ O₃ on the sizing agent. 6.The composition of claim 1 wherein the sizing agent is an alkyl ketenedimer.
 7. The composition of claim 6 wherein the amphoteric polymer ispresent in an amount of from 1 to 35% by weight based on the ketenedimer.
 8. The composition of claim 6 which comprises from about 5 toabout 30% by weight ketene dimer.
 9. A process for the production ofpaper, board or cardboard which comprises utilizing, as a sizing agent,the aqueous composition of claim
 1. 10. An aqueous sizing compositionwhich comprises at least one alkyl ketene dimer, at least one amphotericstarch as a dispersing and/or stabilizing agent for said alkyl ketenedimer, and at least one polyaluminum compound.
 11. The composition ofclaim 10 wherein said amphoteric starch is cationized potato starch. 12.The composition of claim 10 wherein said polyaluminium compound isselected from the group consisting of polyaluminium chloride,sulphate-containing polyaluminium chloride, polyaluminium sulphate, anda mixture or co-condensate of cationic dicyandiamide resin and apolyaluminium compound.
 13. The composition of claim 12 which comprisesfrom about 5 to 30% by weight ketene dimer, from about 1 to 35% byweight amphoteric polymer based on ketene dimer; and from about 0.1 to10% by weight of polyaluminium compound calculated as Al₂ O₃ on thesizing agent.
 14. A method for sizing paper, board or cardboard preparedfrom papermaking stock which comprises adding the composition of claim10 to said papermaking stock prior to forming said papermaking stockinto said paper, board or cardboard.
 15. A method for sizing paper,board or cardboard which comprises applying the composition of claim 10to the surface of said paper, board or cardboard.
 16. The composition ofclaim 10 wherein the amphoteric starch contains cationic groups whichare quaternary ammonium groups and anionic groups which are selectedfrom the group consisting of phosphate, phosphonate, sulfate,sulphonate, and carboxylic acid groups.